1. Field of the Invention
The present invention relates to a camera system consisting of a lens apparatus and an imaging apparatus body enabling removable attachment of the lens apparatus, and to a technology that changes communication methods between the two apparatuses according to shooting modes.
2. Description of the Related Art
In recent years, there has been an ongoing shift from film-type cameras to digital cameras that use imaging elements. In addition to still-image shooting, video shooting has become possible even with so-called single-lens reflex cameras with interchangeable lenses. Now, with respect to the body unit of a single-lens reflex camera, there is not only the type in which a photographic object is viewed using an optical view system including a so-called reflex mirror, but also the type in which viewing is conducted with display of a photographic image on a monitor screen. During video imaging and preview imaging, operation (so-called “wobbling operation”) is conducted in which a focus lens is minutely driven forward or backward from a lens position where the AF (autofocus) evaluation value is at maximum. By this means, the vicinity of the subject can be constantly kept in focus to obtain an optimal focus state.
FIG. 10A and FIG. 10B are explanatory views of wobbling operation in a conventional imaging apparatus. FIG. 10A exemplifies exposure control, and FIG. 10B exemplifies focus lens drive control. Time is represented on the horizontal axis. In wobbling operation, the periods corresponding to light exposure times are the focus lens stoppage periods, and the intervals between these are the drive periods. Users are mostly unaware of focus misalignments, because the focus lens is driven within a range that does not enable discrimination of focus misalignments from captured video images. This technology is disclosed in Japanese Patent Application Laid-Open No. 9-284632.
In contrast to still-image shooting, with video shooting, an actuator in an interchangeable lens must be continuously driven for purposes of focusing, diaphragm driving, and the like. Consequently, it is important to conduct drive control by frequently monitoring the state of the interchangeable lens. Monitoring of the state of an interchangeable lens and drive control of the respective actuator are accomplished by a communication function executed between the interchangeable lens and the camera body. In a conventional communication method, the camera body transmits a communication command requesting lens information to the interchangeable lens. The interchangeable lens sends information corresponding to the aforementioned command received from the camera body at the next communication time. With this communication method, for example, it is necessary for the camera body to transmit to the lens side one command communication to acquire the status of the interchangeable lens, and two more communications for data reception. In short, three communications are required for two data acquisitions. In the case of video shooting, focus correction data and diaphragm value data must be communicated more frequently than in still-image shooting, with the result that wasteful communication increases, and efficiency is reduced.
In Japanese Patent Application No. 2010-511871, a method is proposed in which the appropriate communication method between camera and interchangeable lens is used in still-image shooting mode and in video shooting mode, respectively. In Japanese Patent Application No. 2010-511871, as methods for switching communication methods according to mode, there is disclosure of a changeover method in which the camera transmits a changeover request, and receives a changeover completion notification from the lens, and a changeover method in which changeover is performed at a fixed time after transmission of a changeover request.
In the switching of a conventional communication method, processing time must be shortened. The reason for this is that when communication methods are switched between a video shooting mode and a still-image shooting mode in a camera capable of video shooting and still-image shooting, communication must be conducted multiple times, which takes up processing time. Moreover, with the method in which communication method changeover is performed at a fixed time after changeover request transmission, it is not necessarily the case that communication can always be conducted at a fixed time even with a high-performance lens. In such cases, there is the possibility that changeover processing cannot be rapidly conducted.